This invention pertains to image-producing devices and more specifically to fusing an image to a medium in an image-producing device.
Various types of prior art image-producing devices are known. When I say xe2x80x9cimage-producing devicexe2x80x9d I mean a device that is configured to produce a visual image and further configured to transfer the image to an image medium (medium). One relatively common type of image-producing device is known as a printer. However, it is understood that the term xe2x80x9cimage-producing devicexe2x80x9d includes any type of device, including copiers, facsimile machines, and the like.
Generally, image-producing devices are configured to produce images in one or more colors, including the xe2x80x9ccolorxe2x80x9d of black. These images are typically transferred to a medium which is in the form of paper sheets, although other forms of medium, such as transparencies and the like, are employed.
Image-producing devices usually employ one of several known methods of producing an image. Two popular methods of producing an image are known as xe2x80x9cink jet printingxe2x80x9d and xe2x80x9claser printing.xe2x80x9d Both the ink jet printing method and the laser printing method are well known in the art. As the respective names imply, the ink jet method utilizes at least one jet of ink in producing an image, while the laser method utilizes at least one laser in producing an image.
Each method of producing an image has various advantages. One advantage of the laser method is that the image can be substantially bonded to the medium so as to be relatively smear-proof. That is, the laser method is capable of producing images that are generally known to be substantially fixed to the medium so that the image cannot be easily deformed or smeared. The method of fixing the image to the medium in the laser printing method is sometimes referred to as xe2x80x9cfusingxe2x80x9d the image to the medium.
The laser printing method can be broken down into several steps. A first step is the production of an image on a surface, such as a photoconductor or intermediate transfer surface, which is a component of the image-producing device. This step of producing the image on the surface usually comprises forming the image on the surface by depositing powdered toner onto the surface. A second step of the printing method is the transfer of the toner which makes up the image from the surface to a sheet of medium.
A third step of the printing method is fusing of the image to the sheet of medium. The step of fusing the image to the sheet of medium usually comprises heating the toner and medium to a given temperature to cause the toner to xe2x80x9cfusexe2x80x9d to the medium. Generally, the temperature to which the toner is heated is sufficient to substantially melt the toner into a xe2x80x9cplasticxe2x80x9d state but not to a liquid state. The temperature to which the toner is heated can vary as a function of the composition of the toner. However, the temperature is generally about 190 degrees, Centigrade. The step of heating the toner can also be accompanied by the step of applying pressure to the heated toner to aid in fusing the heated toner to the medium.
With reference to FIG. 1, a schematic view is shown of a typical prior art image-producing device 10. The device 10 typically comprises a production/transfer portion 12 which is configured to produce an image (not shown) and which is also configured to transfer the image onto a sheet of medium xe2x80x9cMxe2x80x9d such as a sheet of paper or the like. The prior art device 10 can also typically comprise a feed mechanism 22 which is configured to feed the medium xe2x80x9cMxe2x80x9d through the device 10 at a substantially constant rate of speed. The feed mechanism 22 can comprise a pair of substantially parallel rollers 24 or the like, between which the medium xe2x80x9cMxe2x80x9d is captured and fed.
The device 10 also typically comprises a medium sensor 32 which is configured to detect the presence of the leading edge xe2x80x9cLExe2x80x9d of the medium xe2x80x9cMxe2x80x9d and can also be configured to detect the trailing edge xe2x80x9cTExe2x80x9d of the medium as well. As shown, the device 10 can also comprise a fusing portion 42 which is configured to substantially fuse the image to the medium xe2x80x9cM.xe2x80x9d When I say xe2x80x9cfusexe2x80x9d I mean a process by which an image is substantially fixed or bonded to a medium, wherein the process is performed in conjunction with the use of an image-producing device.
The fusing portion 42 can comprise a heater 44 as well as a pressure roller 46 between which the medium xe2x80x9cMxe2x80x9d is passed to fuse the image thereto. The pressure roller 46 can be driven by way of a motor or the like (not shown) so as to assist the feed mechanism in moving the medium xe2x80x9cMxe2x80x9d along the feed path xe2x80x9cF.xe2x80x9d In addition, the fusing portion 42 can comprise a temperature sensor 48 which is configured to detect the temperature of the heater 44.
The prior art device 10 can also comprise a controller 52 which is in communication with at least one of the above-described components 12, 22, 32, 42 by way of respective communication links 60. The controller 52 is configured to control various operational aspects of the prior art device 10. The controller 52 can comprise a data storage memory 54 which is configured to store various data. The controller 52 can also include a processing portion 55 which is configured to make operational decisions based on various operational parameters. Various algorithms 56, 57 can also be included in the controller 52. The algorithms 56, 57 can be configured to carry out specific operational functions of the device 10.
The production/transfer portion 12, the feed mechanism 22, the sensor 32, and the fusing portion 42 are supported on a structural base (not shown) or the like so as to each have substantially fixed locations relative to one another. The medium xe2x80x9cMxe2x80x9d is fed through the device 10 along the feed path xe2x80x9cF.xe2x80x9d As mentioned above, the feed mechanism 22 is configured to feed the medium xe2x80x9cMxe2x80x9d through the device 10 and along the feed path xe2x80x9cFxe2x80x9d at a substantially constant rate of speed.
The physical distances along the feed path xe2x80x9cFxe2x80x9d and between the various components is generally know. For example, the distance xe2x80x9cDxe2x80x9d along the feed path xe2x80x9cFxe2x80x9d and between the sensor 32 and the production/transfer portion 12 is known. Because the rate of speed of the medium xe2x80x9cMxe2x80x9d along the feed path xe2x80x9cFxe2x80x9d is known, as well as the distance between the sensor 32 and the production/transfer portion 12, the position of the medium relative to the production/transfer portion can be determined as a function of time.
For example, once the medium xe2x80x9cMxe2x80x9d is captured by the feed mechanism 22, the speed of the medium along the feed path xe2x80x9cFxe2x80x9d is known. The sensor 32 can substantially detect the exact moment that the leading edge xe2x80x9cLExe2x80x9d of the medium xe2x80x9cMxe2x80x9d passes the sensor, at which moment a timer can be started. The quotient of the rate of speed of the medium xe2x80x9cMxe2x80x9d along the feed path xe2x80x9cFxe2x80x9d divided by the distance xe2x80x9cD,xe2x80x9d represents the elapsed time between the moment the leading edge xe2x80x9cLExe2x80x9d passes the sensor 32 and the moment at which the leading edge xe2x80x9cLExe2x80x9d reaches the production/transfer portion 12.
That is, the time at which the leading edge xe2x80x9cLExe2x80x9d reaches the production/transfer portion 12 can be determined by dividing the rate of speed of the medium xe2x80x9cMxe2x80x9d along the feed path xe2x80x9cFxe2x80x9d by the distance xe2x80x9cDxe2x80x9d between the sensor 32 and the production/transfer portion. In this manner, the location of the medium xe2x80x9cMxe2x80x9d along the feed path xe2x80x9cF,xe2x80x9d and relative to the production/transfer portion 12, can be determined. The location of the medium xe2x80x9cMxe2x80x9d along the feed path xe2x80x9cFxe2x80x9d can be essential for the accurate placement of the image onto the medium by the production/transfer portion 12.
After the image is transferred to the medium xe2x80x9cMxe2x80x9d at the production/transfer portion 12, the medium continues along the feed path xe2x80x9cFxe2x80x9d to the fusing portion 42 where the image is fused to the medium. As discussed above, the fusing portion 42 comprises a heater 44 and a pressure roller 46. The medium xe2x80x9cMxe2x80x9d travels along the feed path xe2x80x9cFxe2x80x9d and between the heater 44 and the pressure roller 46 as the image is fused to the medium.
Typically, the fusing portion 42 is configured so that the heater 44 is maintained at a temperature set point as a sheet of medium feeds through the fusing portion. By xe2x80x9ctemperature set pointxe2x80x9d I mean a given temperature at which the heater surface is maintained. In prior art devices such as the device 10, the temperature set point is generally substantially constant with respect to any given sheet of medium xe2x80x9cM.xe2x80x9d That is, the temperature set point of prior art devices is configured to remain substantially constant as a given sheet of medium xe2x80x9cMxe2x80x9d feeds through the fusing portion 42.
The temperature set point is usually maintained by way of a feedback control loop or the like. Feedback control loops are well known in the art and are generally employed to automatically maintain an ideal, or xe2x80x9ctarget,xe2x80x9d operational parameter of a given system in response to unpredictable external factors which affect the operational parameter. Feedback control loops typically employ at least one sensor which is configured to detect and measure an actual characteristic of the operational parameter in order to compare the actual characteristic to an ideal characteristic. One well-know example of a feedback control loop is the temperature control system of a residential heating system. This system is often referred to as a xe2x80x9cthermostat.xe2x80x9d
The thermostat acts as a feedback control loop to maintain the inside temperature of a house within a given range and in response to external, ambient temperatures. The ambient temperature affects the rate of heat loss through the walls of the house. That is, relatively low, or cold, ambient temperatures result in a greater rate of heat loss through the walls of the house as compared to relatively higher, or warmer, ambient temperatures. As heat is lost through the walls of a house, the interior temperature of the house falls. The thermostat acts as a sensor to monitor the interior temperature of the house.
When the thermostat detects that the interior temperature has fallen below a given minimum acceptable point, the thermostat causes the heating unit to begin producing heat which is distributed within the interior of the house so as to raise the interior temperature. The heating unit is usually caused to operate until the interior temperature rises to a given maximum temperature at which time the heating unit stops producing heat. The maximum temperature is generally several degrees higher than the minimum acceptable temperature. This process is repeated indefinitely as the heat is lost through the walls of the house.
The ideal temperature, at which the thermostat is set, is usually midway between the minimum acceptable temperature and the maximum temperature. The range between the minimum acceptable temperature and the maximum temperature is usually determined as the result of a compromise between the ability to maintain a comfortable interior temperature and an excessive rate of on/off cycling of the heating unit.
In other words, as the range between the maximum temperature and the minimum acceptable temperature is increased, the heating unit will cycle on and off less frequently, but the interior of the house will be subject to a greater variation of temperatures. On the other hand, as the range between the maximum and minimum temperatures decreases, the interior temperature will remain closer to the ideal temperature, but the heating unit will cycle on and off frequently.
Referring to FIG. 1, the feedback control loop of the fusing portion 42 can operate in a manner similar to the example discussed above. The heat sensor 48 can be configured to detect the temperature of the heater 44. The heat sensor 48 can then convert the detected temperature to a signal which is sent by way of the respective communication link 60 to the controller 52. The controller 52 can receive the signal and read the temperature.
The controller 52 can then compare the detected temperature of the heater 44 to the ideal xe2x80x9ctemperature set pointxe2x80x9d which can be stored or programmed into the controller. If the controller 52 determines that the detected temperature of the heater 44 is below the set point, then the controller sends a signal to the heater which instructs the heater to increase its temperature by producing heat. Conversely, if the controller 52 determines that the detected temperature of the heater 44 is above the set point, then the controller instructs the heater to stop producing heat. Thus, the controller 52, in conjunction with the heat sensor 48, can act as a feedback control loop to maintain the temperature of the heater 44 at, or substantially near, the temperature set point.
Turning now to FIG. 2, a prior art flow diagram 70 is shown. The flow diagram 70 represents one possible prior art control scheme for controlling the fusing portion 42 (shown in FIG. 1) in conjunction with the overall operation of the prior art image-producing device 10 (also shown in FIG. 1). It is understood that many variations of flow diagram 70 are possible. With reference to both FIGS. 1 and 2, the flow chart 70 begins at step S71. In step S72, the controller 52 is notified that medium xe2x80x9cMxe2x80x9d is ready to proceed through the device 10 along the feed path xe2x80x9cF.xe2x80x9d
In accordance with step S73, and in preparation for allowing the medium xe2x80x9cMxe2x80x9d to proceed along the feed path xe2x80x9cF,xe2x80x9d the controller 52 sends a signal to the heater 44 which instructs the heater to increase its temperature to the temperature set point. Moving to step S74, the temperature of the heater 44 is monitored. When the heater 44 attains the temperature set point, the medium xe2x80x9cMxe2x80x9d is allowed to proceed into the device 10 and along the feed path xe2x80x9cF.xe2x80x9d
The next step in the flow diagram is step S75 in which the temperature of the heater 44 is monitored. Corrections to the temperature of the heater 44 are made as necessary in order to maintain the heater at the temperature set point. During step S75, medium continues to proceed through the device 10 along the feed path xe2x80x9cF.xe2x80x9d The step S76 queries whether more medium is to be processed through the device 10.
If the answer to the query of step S76 is xe2x80x9cyes,xe2x80x9d then the path of the flow diagram returns to the previous step of S75, wherein the temperature of the heater 44 is monitored and maintained at the temperature set point. However, if the answer to the query of step S76 is xe2x80x9cno,xe2x80x9d then the flow diagram moves to the next step which is step S77. In step S77 the controller 52 instructs the heater 44 to shut off. The flow diagram ends with the next step, which is step S78.
Referring again to FIG. 1, it is evident that the heater 44 is located in very close proximity to the pressure roller 46. Moreover, it is preferable in most cases for the heater 44 and the pressure roller 46 to be resiliently biased against one another to ensure optimal heat transfer from the heater 44 to the medium xe2x80x9cMxe2x80x9d during fusing of the image thereto. The heater 44 and pressure roller 46 can be resiliently biased against one another through the incorporation of a spring or the like (not shown). Thus, when no medium xe2x80x9cMxe2x80x9d is between the heater 44 and the pressure roller 46, there is contact there between.
As a result of the contact between, or at least the close proximity of, the heater 44 and the pressure roller 46, heat energy is transferred from the heater 44 to the pressure roller 46. That is, when the heater 44 is producing heat energy, the temperature of the pressure roller 46 increases due to the contact between, or close proximity of, the heater and the pressure roller. However, this increase in temperature of the pressure roller 46 occurs only when no medium xe2x80x9cMxe2x80x9d is feeding through the fusing portion 42 and between the heater 44 and the pressure roller.
As discussed above, the temperature the heater 44 is maintained in a substantially precise temperature set point. The substantially precise temperature set point is necessary in order to optimize the fusing process in which a substantially precise quantity of heat is required to properly fuse the image to the medium xe2x80x9cM.xe2x80x9d As is evident from the above discussion for FIG. 2, the heater 44 must generally be at, or substantially near, the temperature set point before the medium xe2x80x9cMxe2x80x9d is allowed to proceed through the fusing portion. This is to ensure that the correct amount of heat energy is available to be transferred to the image and to the medium xe2x80x9cMxe2x80x9d as the medium and image are passed through the fusing portion 42 so as to fuse the image to the medium.
At a minimum, the heater 44 and the pressure roller 46 are in contact with, or in close proximity to, each other for a period of time during which the temperature of the heater is increased to the temperature set point. Thus, before the medium xe2x80x9cMxe2x80x9d feeds along the feed path xe2x80x9cFxe2x80x9d and between the heater 44 and the pressure roller 46, the pressure roller will have attained a temperature which is not negligible. That is, at the time the heater 44 attains the temperature set point, the pressure roller 46 has absorbed a significant amount of heat energy from the heater.
Immediately prior to the entry of the leading edge xe2x80x9cLExe2x80x9d of the medium xe2x80x9cMxe2x80x9d into the device 10, the medium is at a temperature which is substantially equal to the ambient temperature. Since a typical temperature set point is about 190 degrees, Centigrade, the ambient temperature is generally much less than the temperature of the heater 44, and is typically less than 30 degrees, C. As the medium xe2x80x9cMxe2x80x9d is fed through the fusing portion 42, the heater 44 transfers heat to the much cooler medium to raise the temperature of the medium and the image for the fusing thereof. As the heater 44 loses heat energy to the medium xe2x80x9cM,xe2x80x9d the controller 52 maintains the temperature set point by controlling the quantity of heat produced by the heater as discussed above.
As discussed above, the pressure roller 46 is at a significantly high temperature relative to the medium xe2x80x9cMxe2x80x9d when the medium begins to pass between the heater 44 and the pressure roller. The temperature of the pressure roller 46 can be substantially near the temperature set point, although it can also be somewhat less than the temperature set point. In any case, the temperature of the pressure roller 46 will generally be significantly greater than the temperature of the medium xe2x80x9cMxe2x80x9d when the medium first begins to pass between the heater 44 and the pressure roller.
Because the temperature of the pressure roller 46 is greater than the medium xe2x80x9cM,xe2x80x9d heat energy is transferred from the pressure roller 46 to the medium as the medium passes between the heater 44 and the pressure roller. That is, the medium xe2x80x9cMxe2x80x9d absorbs heat energy from both the heater 44 on one side and the pressure roller 46 on the opposite side. However, unlike the heater 44 which remains at the temperature set point as the medium xe2x80x9cMxe2x80x9d passes through the fusing portion 42, the temperature of the pressure roller 46 decreases as heat energy is transferred from the pressure roller to the medium. In other words, the temperature of the pressure roller 46 decreases as a function of the position along the feed path xe2x80x9cFxe2x80x9d of the medium xe2x80x9cMxe2x80x9d relative to the fusing portion 42.
More specifically, as the medium xe2x80x9cMxe2x80x9d passes farther through the fusing portion 42, the temperature of the pressure roller 44 gets lower. This is because the pressure roller 46 absorbs heat energy from the heater 44 only when the medium xe2x80x9cMxe2x80x9d is not between the heater and the pressure roller, and if the portion of the medium immediately adjacent to the pressure roller is at a temperature that is lower than that of the pressure roller. Conversely, when the medium xe2x80x9cMxe2x80x9d is between the heater 44 and the pressure roller 46, heat is transferred from both of the relatively hot heater 44 and relatively hot pressure roller 46 to the relatively cool medium xe2x80x9cM.xe2x80x9d After the trailing edge xe2x80x9cTExe2x80x9d of the medium xe2x80x9cMxe2x80x9d passes completely through the fusing portion 42, the pressure roller 46 again absorbs heat energy from the heater 44, which causes the temperature of the pressure roller to again increase.
Because the temperature of the pressure roller 46 decreases as the medium xe2x80x9cMxe2x80x9d passes through the fusing portion 42, the capacity of the pressure roller to transfer heat energy to the medium xe2x80x9cMxe2x80x9d decreases as well. In turn, because the heat transfer capacity of the pressure roller 46 decreases as the medium passes through the fusing portion 42, the leading edge xe2x80x9cLExe2x80x9d of the medium xe2x80x9cMxe2x80x9d absorbs more heat energy than the trailing edge xe2x80x9cTE.xe2x80x9d
Generally, the quantity of heat energy absorbed by the medium xe2x80x9cMxe2x80x9d at a given position thereon is inversely proportional to the distance between the given position and the leading edge xe2x80x9cLExe2x80x9d of the medium. For example, a given position on the medium xe2x80x9cMxe2x80x9d that is substantially midway between the leading edge xe2x80x9cLExe2x80x9d and the trailing edge xe2x80x9cTExe2x80x9d will absorb a given quantity of heat energy that is less than the quantity of heat energy that is absorbed by the medium at the leading edge, and more than the quantity of heat absorbed by the medium at the trailing edge.
As indicated by the above discussion, the medium xe2x80x9cMxe2x80x9d absorbs heat energy in varying quantities during the fusing process, wherein the quantity of heat absorbed by the medium is dependent upon the extent that the medium has passed through the fusing portion 42. That is, as the medium passes through the fusing portion 42, the quantity of heat transferred to the medium xe2x80x9cMxe2x80x9d from the fusing portion decreases due to the decreasing temperature of the pressure roller 46. This can result in inconsistent adhesion of the image to the medium xe2x80x9cMxe2x80x9d because, at best, only a portion of the image can be exposed to the optimum quantity of heat energy.
As is evident, problems are associated with the use of prior art image-producing devices which incorporate the above-illustrated fusing methods and apparatus. What is needed then, are methods and apparatus which achieve the benefits to be derived from similar prior art devices, but which avoid the shortcomings and detriments individually associated therewith.
The invention includes methods and apparatus for fusing images to medium in conjunction with the use of an image-producing device.
In accordance with a first embodiment of the present invention, an apparatus for fusing an image to a medium comprises a heat source to which the image and medium is exposed as the medium and image are fed through an image-producing device. The heat source is configured to increase in temperature as the medium and image are exposed thereto.
In accordance with a second embodiment of the present invention, a method of fusing an image to a medium includes providing a heat source and increasing the temperature of the heat source while the image and medium are exposed to the heat source.
In accordance with a third embodiment of the present invention, another method of fusing an image to a medium includes providing a heat source and a pressure roller. The image and medium is passed between the pressure roller and the heat source while the temperature of the heat source is increased.